The location an properties of the replication terminus if the chromosome of Escherichia coli are being determined. DNA-DNA hybridization using various E. coli F' episome DNA and DNA obtained from bacteriphage lambda specialized transducing phage are used to determine how much replication occurs in regions of the chromosome near the replication terminus. The replication is being studied in cells that contain prophage P2sig5. This phage has been inserted in a site near the metG locus (min 46) or the gal locus (min 17) and induction of the prophage causes the initiation of replication forks that approach the terminus from the counterclockwise and clockwise direction, respectively, on the genetic map. These procedures have demonstrated that the terminus is near the rac locus (min 31) and the location is now being determined with greater precision. These strains and procedures are also being used to determine if the terminus is attached to the cell membrane. The terminus region is also being studied by autoradiography. The main purpose of this type of exeriment is to determine how much is in the blank region of the genetic map that surrounds the terminus.